The present invention relates generally to electrically driven implements such as mowers, and, more specifically, to a circuit for switching and adjusting high currents to the motors of such implements.
Electrically driven implements such as reel-type lawn mowers are becoming increasingly popular. Switching the motors on and off and controlling the relatively high currents to such motors is a continuing source of problems. Expensive controllers are required to handle the high inrush current and the high voltage transients that are created when current is interrupted. Systems utilizing contact or transistor DC switching are subject to arcing and high voltage transients and associated RFI problems. Such systems are also difficult to control to maintain a constant speed and/or voltage output. In the hostile environment encountered; by a typical high current draw implement such as an electrically driven mower or similar implement, the problems become particularly acute. Smooth or xe2x80x9csoftxe2x80x9d starting of the controlled motors is difficult or impossible to achieve with at least most presently available systems.
It is therefore an object of the present invention to provide an improved control system for electrically driven implements. It is a further object to provide such a system which overcomes most or all of the aforementioned problems.
It is another object of the present invention to provide an improved control system for electrically driven implements which is less expensive and more reliable than at least most previously available systems. It is a further object to provide such a system which reduces or eliminates arcing and radio interference problems typically associated with high current DC switching.
It is still another object of the present invention to provide an improved control system for an electrically driven implement which is low in cost, eliminates high current switching problems and facilitates smooth, gradual starting of the electrical motors. It is another object to provide such a system which eliminates the need for high current contact or switching transistors and which can be controlled from a relatively low level logic signal or can be ramped up and down without subjecting the system to arcing and RFI problems.
It is a further object of the invention to provide an improved DC motor load controller for an implement utilizing control of the alternator field to control alternator output for switching and voltage control. It is a further object to provide such a system wherein the field control is also responsive to interlocks on the implement.
A load controller constructed in accordance with the teachings of the present invention includes an alternator with a field regulator having additional inputs connected to a main intelligent control which includes interlock circuitry. The additional inputs provide both an on/off or voltage select function and an interlock function. Relatively high current load motors, such as mower reel drive motors, are connected to the alternator output. Rather than utilizing expensive contact or switching transistors for directly switching and adjusting high current loads at the alternator output, a lower cost and lower current field regulator circuit provides switching and load control and eliminates high inrush currents and current and high voltage transients. On/off functions and level control functions therefore can be provided from a logic level signal, and the motors can be started smoothly by bringing the voltage up gradually. The system eliminates arcing and RFI problems associated with such arcing. The interlock input function input helps integrate the implement system for convenient, reliable and low cost control.